1. Field of the Invention
The present invention relates to a bi-directional clutch.
2. Description of the Related Art
A conventional bi-directional clutch has a structure as shown in FIG. 7, which shows a sectional view of the essential portion of the clutch. A bi-directional clutch 51 is constituted so that a gourd-shaped sprag 55 is disposed within a retainer 54 between an outer ring 52 and an inner ring 53 and is biased by a spring plate 56. When the outer ring 52 rotates in a normal direction indicated by an arrow a in FIG. 7, the retainer 54 rotates in a reverse direction relative to the outer ring, so that the sprag 55 is tilted toward the rotational direction of the outer ring 52. Therefore, an upper surface and a lower surface of the sprag 55 contact with the outer ring 52 and the inner ring 53, respectively, so as to form a wedge. As a result, the inner ring 53 rotates idle in a direction indicated by an arrow b, which is the same direction as the rotational direction of the outer ring 52.
On the other hand, the clutch is constituted so that the sprag 55 is tilted to the reverse direction, when the outer ring 52 is rotated in the reverse direction as shown in FIG. 8. As a result, the inner ring 53 rotates idle in the same direction as that of the outer ring 52, or the direction indicated by the arrow b. It should be noted that the inner ring 53 may be locked in rotational directions indicated by arrows c in FIG. 7 and FIG. 8.
In the conventional bi-directional clutch 51 employing the sprag 55, when the sprag 55 is abruptly tilted by the application of an excessive torque, the height of the sprag 55 may be abruptly reduced, so that a roll-over (an excessive tilting) phenomenon occurs. As a result, when an excessive torque is loaded, a problem may be caused that the rotational force of the outer ring 52 cannot be properly transmitted to the inner ring 53, or that the transmission of rotation between the outer ring 52 and the inner ring 53 cannot be properly interrupted.
The present invention has been contemplated in consideration of the above problems.
It is an object of the present invention to provide a bi-directional clutch, which does not cause a roll-over phenomenon.
According to the present invention, a bi-directional clutch comprises an outer ring, an inner ring and a roller. The roller is retained by a retainer and is positioned between the outer ring and the inner ring. The outer ring has a cam surface, so that the roller forms a wedge that contacts the outer ring and the inner ring. Therefore, the inner ring can be rotated in the same direction as the outer ring. The roller does not cause a roll-over phenomenon that may be caused by the conventional clutch incorporating sprags. Therefore, the rotational force of the outer ring can be properly transmitted to the inner ring, or the transmission of power between the outer ring and the inner ring can be properly interrupted.
Preferably, the cam surface includes a first cam surface for a normal rotation and a second surface for a reverse rotation. Therefore, when the outer ring rotates in either the normal direction or the reverse direction, the roller can form a wedge so as to rotate the inner ring in the same direction as the outer ring.
Preferably, the bi-directional clutch further includes a stopper surface at one end of the cam surface. The roller contacts the stopper surface when a load torque exceeds a set load torque, so that the stopper surface functions as a torque limiter. Therefore, when a large load is applied, the roller contacts the stopper surface, so that a strut angle increases to cause a slip. As a result, an excessive load can be favorably prevented.